1. Field of the Invention
The present invention relates to a plasma chemical vapor deposition method in which plasma is produced by a deposition material gas and a film is formed or deposited on a substrate in the plasma, and also relates to a plasma chemical vapor deposition apparatus for executing the above method.
In this specification and appended claims, the plasma chemical vapor deposition is referred to as "plasma-CVD"
2. Description of the Background Art
Plasma-CVD has been utilized for many purposes such as manufacturing of thin film transistors, manufacturing of various kinds of semiconductor devices such as sensors utilizing semiconductor materials, manufacturing of various kinds of thin film devices used in solar batteries, LCDs (liquid-crystal displays) and others, formation of ferroelectric films used, for example, in flash memories, gas sensors and thin film capacitor, formation of carbon films for loudspeaker diaphragms, coating of ornaments and decorations, and formation of films having a wear resistance for machine parts, tools and others requiring a wear resistance.
Various types of apparatuses performing the plasma-CVD have been known.
As a typical example, a parallel plated plasma-CVD apparatus utilizing radio-frequency power will be described below with reference to FIGS. 15 and 16. In the following description and appended claims, "radio-frequency" and "radio-frequency power" is referred to as "rf" and "rf-power", respectively, and plasma-CVD using the rf-power is referred to as "rf plasma-CVD".
In the apparatus shown in FIG. 15, two electrodes for producing plasma are arranged parallel to each other in the longitudinal direction. The apparatus shown in FIG. 16, two electrodes for producing plasma are arranged parallel to each other in the lateral direction. These apparatuses have the substantially same structure and operation except for arrangement of the electrodes and other several portions. Parts and portions having the substantially same function bear the same reference numbers.
Each of the plasma-CVD apparatuses shown in FIGS. 15 and 16 includes a vacuum container 10 used as a process chamber, in which an electrode 20 also serving as a substrate holder for holding a substrate S10, on which a film is to be deposited, as well as an electrode 30 are arranged in an opposed fashion.
The electrode 20 is generally a ground electrode, and is additionally provided with a heater 210 for heating the substrate S10 disposed thereon to a deposition temperature. If radiant heat is used to heat the substrate S10, the heater 210 is spaced from the electrode 20.
The electrode 30 is a power application electrode which applies the rf-power to the film deposition gas, i.e., gas for film formation or deposition, introduced between the electrodes 20 and 30 so as to convert the gas into the plasma. In these examples, the electrode 30 is connected to an rf-power source 320 via a matching box 310.
An exhaust pump 520 is connected to the process chamber 10 via a valve 510, and a gas source 40 for the film deposition gas is connected thereto via a piping. The gas source 40 includes one or more mass-flow controllers 411, 412, . . . , one or more valves 421, 422, . . . connected to the mass-flow controllers, respectively, and one or more film deposition gas sources 431, 432, . . . connected to the valves, respectively.
According to the parallel plated plasma-CVD apparatuses described above, the substrate S10 is transferred by an unillustrated substrate transfer device into the process chamber 10 and mounted on the electrode 20. The valve 510 is opened and the exhaust pump 520 is driven to set the process chamber 10 to a predetermined degree of vacuum, and the film deposition gas is supplied into the chamber 10 from the gas source 40. The power source 320 applies the rf-power to the rf-electrode 30. Thereby, the introduced gas forms plasma, in which an intended film is deposited on the surface of the substrate S10.
For example, the pressure in the process chamber 10 is set to about hundreds of millitorrs, and the heater 210 heats the substrate holder electrode 20 to a temperature of about 300.degree. C. The substrate S10 is mounted on the electrode 20, and the gas source 40 supplies predetermined amounts of monosilane (SiH.sub.4) gas and hydrogen (H.sub.2) gas, and the rf-power of a frequency of 13.56 MHz is applied to the electrode 30. Whereby, the gases form the plasma, and an amorphous silicon film is deposited on the substrate S10. A predetermined amount of ammonia (NH.sub.3) gas may be introduced instead of the hydrogen gas, in which case a silicon nitride film is formed.
Another processing may be executed as follows. The pressure in the process chamber 10 is approximately set to hundreds of millitorrs, the substrate holder electrode 20 is heated by the heater 210, and the substrate S10 is mounted on the electrode 20. The gas source 40 supplies only a predetermined amount of hydrocarbon compound gas such as a methane (CH.sub.4) gas or a ethane (C.sub.2 H.sub.6) gas, or predetermined amounts of the above hydrocarbon compound gas and hydrogen (H.sub.2) gas. An rf-power of a frequency, e.g., of 13.56 MHz is applied to the electrode 30. Whereby, the gas forms plasma, and a thin carbon film is deposited on the substrate S10. In this case, the film quality can be controlled by changing the processing temperature of the substrate S10. For example, if the film is to be deposited on the substrate made of synthetic resin such as polyimide resin, the substrate is set to a temperature of about 100.degree. C. or less considering heat resistance of the substrate, in which case a diamond like carbon (will be also referred to as "DLC") film is deposited. The DLC film is used as a diaphragm of a loudspeaker, coating of an decoration and others.
A plasma-CVD apparatus shown in FIG. 17 is also well known.
This apparatus can use a safe material, which is liquid in an ambience of room temperature of, e.g., 25.degree. C., for depositing even such a film that requires the plasma-CVD apparatuses shown in FIGS. 15 and 16 to use a dangerous gas such as flammable gas or explosive gas for depositing the film.
For example, in order to form the amorphous silicon film or silicon nitride film, the plasma-CVD apparatuses in FIGS. 15 and 16 use the monosilane (SiH.sub.4) gas as described above. However, the SiH.sub.4 gas is legally designated as a dangerous (e.g., flammable or explosive) special material gas, so that a significantly expensive countermeasure for safety is required for using the silane gas. For this reason, the apparatus shown in FIG. 17 is used. More specifically, when the amorphous silicon film is to be formed, a gas of silicon tetrachloride (SiCl.sub.4), which is liquid at room temperature, and a hydrogen gas are used. When the silicon nitride film is to be formed, the silicon tetrachloride (SiCl.sub.4) gas and an ammonia (NH.sub.3) gas are used.
When silicon tetrachloride (SiCl.sub.4) is used, SiCl.sub.4 is stored in a bubbler 44, as shown in FIG. 17, and is bubbled to supply it to the process chamber 10. More specifically, in the apparatus shown in FIG. 17, a gas supply unit 400 which is connected to the process chamber 10 via a piping includes the sealedly closable container (bubbler) 44, which is connected to a gas source 453 of a carrier gas via a mass-flow controller 451 and a valve 452. A piping extending from the mass-flow controller 451 has an end located at the vicinity of the bottom of the bubbler 44. An upper space in the bubbler 44 is connected to the process chamber 10 via a piping. In order to prevent condensation of the SiCl.sub.4 gas vaporized in the bubbler 44, heaters 401 and 402 are associated to the bubbler 44 and the piping between the bubbler 44 and the process chamber 10, respectively. If necessary, the process chamber 10 may be connected to a gas source(s) 463, 473, . . . storing other material gas(es) via one or more mass-flow controllers 461, 471, . . . and valves 462, 472, . . . , respectively. Structure other than the above is the same as those shown in FIG. 16, and the same parts and portions as those in FIG. 16 bear the same reference numbers.
In the process of forming, e.g., an amorphous silicon film by the above plasma-CVD apparatus, the substrate S10 is mounted on the ground electrode 20, and is heated to about 500.degree. C. by the heater 210. Liquid SiCl.sub.4 is stored in the bubbler 44, and a vacuum pressure is applied into the process chamber 10 by the pump 520, so that hydrogen gas is introduced from the gas source 453 into the bubbler 44 for bubbling the SiCl.sub.4, and the generated SiCl.sub.4 gas is supplied to the process chamber 10. The bubbling may be performed, for example, with a hydrogen (H.sub.2) gas or an inert carrier gas such as argon (Ar) gas or helium (He) gas supplied from a gas source, and hydrogen gas may be supplied from another gas source such as source 463. The power source 320 applies the rf-power to the gas introduced into the process chamber 10 to form plasma from the gas, and the amorphous silicon film is deposited on the substrate S10 in the plasma. If the temperature of substrate is set to 800.degree. C. or more, a polycrystalline silicon (will be also referred to as "p-Si") film or a single crystal silicon film can be formed.
A plasma-CVD apparatus shown in FIG. 18 has also been known.
This apparatus has also been known as a parallel plated rf plasma-CVD apparatus, and includes, as a process chamber, a vacuum container 1A, in which an electrode 2A also serving as a substrate holder for carrying the substrate S10 is disposed together with an electrode 3A opposed to the electrode 2A.
The electrode 2A is generally grounded, and is provided with a heater 21A for heating the substrate S10 mounted thereon to a film deposition temperature. If radiation heat is used for heating the substrate S10, the heater 21A is separated from the electrode 2A.
The electrode 3A functions as a power application electrode for applying the power to the film deposition gas introduced between the electrodes 2A and 3A so as to form plasma. In the illustrated prior art, the electrode 3A is connected to an rf-power source 32A via a matching box 31A. A heater 33A is associated to the electrode 3A for maintaining the gaseous state of the deposition material gas introduced between the electrodes 2A and 3A, even if the apparatus uses the gas which is liquid at room temperature. The heater 33A may be separated from the electrode 3A.
The process chamber 1A is connected to an exhaust pump 42A via a valve 41A, and is connected via a piping to a gas supply unit 5A for supplying a pretreatment gas and a film deposition gas. The gas supply unit 5A can supply the film deposition gas of compound such as silicon tetrachloride (SiCl.sub.4), which is liquid at room temperature, to the process chamber 1A by bubbling such a compound. For this purpose, the gas supply unit 5A is formed of a bubbler unit 51A for supplying the gas of the compound which is liquid at a room temperature, and a gas supply portion 52A for supplying the gas of compound which is gaseous at room temperature.
The bubbler unit 51A is provided with one or more sealedly closable containers (bubblers) 51a1, 51a2, . . . , which are connected to gas sources 51d1, 51d2, . . . of carrier gases via mass-flow controllers 51b1, 51b2, . . . and valves 51c1, 51c2, . . . , respectively. Ends of pipings extending from the mass-flow controllers 51b1, 51b2, . . . are located near the bottom of the bubblers 51a1, 51a2, . . . , respectively.
Upper spaces in the bubblers 51a1, 51a2, . . . are connected to the process chamber 1A via valves 51e1, 51e2, . . . and pressure regulators 51f1, 51f2, . . . Each of the pressure regulators 51f1, 51f2, . . . is formed of a pressure regulator valve and a pressure gauge. Temperature controllers 51g1, 51g2, . . . each including a heater and a Peltier element are associated to the bubblers 51a1, 51a2, . . . , respectively. A heater 51h is provided at the piping extending from the bubblers 51a1, 51a2, . . . to the process chamber 1A.
The gas supply unit 52A includes one or more gas sources 523a, 523b, . . . as well as mass-flow controllers 521a, 521b, . . . and valves 522a, 522b, . . . associated thereto for supplying a gas such as a film deposition gas, a pretreatment gas and, if necessary, a carrier gas or the like, which are gaseous at room temperature, to the process chamber 1A.
In the operation of depositing an amorphous silicon film on the substrate S10 by the above plasma-CVD apparatus, the substrate S10 is transferred into the process chamber 1A, and is mounted on the electrode 2A which is heated to about 500.degree. C. by the heater 21A. Then, the valve 41A is operated and the exhaust pump 42A is driven to set the chamber 1A to an intended degree of vacuum of about hundreds of millitorrs. The gas supply portion 52A in the gas supply unit 5A supplies a hydrogen (H.sub.2) gas as a pretreatment gas, and the power source 32A applies the rf-power to the rf-electrode 3A for a predetermined time period. Thereby, plasma is formed from the hydrogen gas, and the surface of the substrate S10 is cleaned in the plasma. Then, the carrier gas, i.e., hydrogen gas is introduced from the gas source 51d1 into the bubbler 51a1 storing liquid silicon tetrachloride (SiCl.sub.4) for bubbling the liquid silicon tetrachloride, and the SiCl.sub.4 gas thus generated is supplied into the process chamber 1A. In this operation, the bubbler 51a1 is heated by the heat controller 51g1 to about 50.degree.-70.degree. C. If necessary, the piping between the bubbler 51a1 and the chamber 1A is heated by the heater 51h to an appropriate temperature, and likewise the electrode 3A is heated by the heater 33A. At the same time, the power source 32A applies the rf-power to the rf-electrode 3A, so that plasma is formed from the introduced gas, and the amorphous silicon film is formed on the surface of the substrate S10. Bubbling may be carried out, for example, with a hydrogen gas or an inert gas such as a helium (He) gas or an argon (Ar) gas, and hydrogen gas may be supplied via another passage from the gas supply unit 52A.
In the deposition method and apparatus described above, a polycrystalline silicon film or a single crystal silicon film is deposited if the substrate is maintained at a temperature of 800.degree. C. or more during the deposition. In the deposition process, if the bubbling is carried out with a hydrogen gas, and the gas supply unit 52A introduces an ammonia (NH.sub.3) gas into the chamber 1A, a silicon nitride film is deposited. In the deposition process, a hydrogen gas or a nitrogen (N.sub.2) gas may be introduced as a carrier gas into the bubbler storing, as film material, titanium tetrachloride (TiCl.sub.4), and an ammonia gas may be introduced from the gas supply unit 52A into the chamber 1A, in which case a titanium nitride film is deposited. If the deposition is carried out at a relatively low temperature, a monosilane (SiH.sub.4) gas and a hydrogen gas can be used to deposit an amorphous silicon film without using a film material which is liquid at a room temperature, and likewise a monosilane gas and an ammonia gas can be used to deposit a silicon nitride film.
Several prior arts of the plasma-CVD have been described. Now, formation of a ferroelectric film in the prior art will be described below, because the invention also relates to the formation of the ferroelectric film.
In general, the ferroelectric film is formed by a thermal chemical vapor deposition (thermal-CVD) method. A typical example of the thermal-CVD apparatus for this film formation is shown in FIG. 19.
This apparatus has a process chamber 1 as well as a load lock chamber 3 connected to the chamber 1 via a gate valve a. In the process chamber 1, there is arranged a substrate holder 4 for holding the substrate S10, and the substrate holder 4 is provided with a high-temperature plate heater 41 heating the substrate mounted on the substrate S10 to a film deposition temperature. If radiation heat is used for heating the substrate S10, the heater 41 is separated from the holder 4.
The process chamber 1 is also connected to an exhaust device 6, which includes a valve 61, a turbo molecular pump 62, a valve 63 and a rotary pump 64 connected in this order.
The process chamber 1 is also connected to a gas supply unit 2. For forming a ferroelectric film, one generally uses an organic compound gas containing element of the intended ferroelectric film as well as another kind of gas which contains oxygen and is different from the organic compound gas. In many cases, the organic compound is liquid at a room temperature. Therefore, the gas supply unit 2 can supply the organic compound into the process chamber 1 by bubbling it. For this purpose, the gas supply unit 2 is formed of a bubbler unit 21 for supplying the organic compound, which is liquid at a room temperature, and a different gas supply unit 22 for supplying the different kind of gas.
The bubbler unit 21 is provided with one or more sealedly closable containers or bubblers 21a1, 21a2, . . . , which are connected to gas sources 21d1, 21d2, . . . of carrier gases via mass-flow controllers 21b1, 21b2, . . . and valves 21c1, 21c2, . . . , respectively. Ends of pipings extending from the mass-flow controllers 21b1, 21b2, . . . are located near the bottoms of the bubblers 21a1, 21a2, . . . , respectively. Upper spaces in the bubblers 21a1, 21a2, . . . . are connected to the process chamber 1 via pipings provided with valves 21e1, 21e2, . . . and pressure regulators 21f1, 21f2, . . . . Each of the pressure regulators 21f1, 21f2, . . . . is formed of a pressure regulator valve and a pressure gauge. Temperature controllers 21g1, 21g2, . . . each including a heater and a Peltier element are associated to the bubblers 21a1, 21a2, . . . . A heater 21h is associated to the pipings between the bubblers 21a1, 21a2, . . . and the process chamber 1.
The different gas supply unit 22 contains one or more gas sources 223a, 223b, . . . of different kinds of gases which are connected to the chamber 1 via mass-flow controllers 221a, 221b, . . . and valves 222a, 222b, . . . , so that a gas containing oxygen and, if required, a different kind of gas such as a carrier gas can be supplied into the process chamber 1.
The load lock chamber 3 is provided with a gate valve b which can be externally opened. A lamp heater 31 for preheating the substrate S10 is arranged in the chamber 3. The chamber 3 is connected to an exhaust device 8. The exhaust device 8 is formed of a valve 81, a turbo molecular pump 82, a valve 83 and a rotary pump 84 connected in this order, and the rotary pump 84 is also connected to the chamber 3 via a valve 85. When a vacuum pressure is to be applied to the load lock chamber 3 at the atmospheric pressure, only the valve 85 is opened and the rotary pump 84 is driven. Once a predetermined degree of vacuum is attained, the valve 85 is closed, the valves 81 and 83 are opened, and the rotary pump 84 and the turbo molecular pump 82 are driven to maintain the vacuum pressure.
In the operation of depositing ditantalum pentoxide (Ta.sub.2 O.sub.5) film on the substrate by the above thermal-CVD apparatus, the substrate S10 is transferred through the gate valve b into the load lock chamber 3 heated by the lamp heater 31. Then, the gate valve b is closed, and the exhaust device 8 is driven to attain the predetermined degree of vacuum in the chamber 3. Then, the substrate S10 is transferred through the gate valve a into the process chamber 1 which is maintained at the predetermined degree of vacuum for film deposition, i.e., from about hundreds millitorrs to about several torrs by driving the exhaust device 6, and is mounted on the substrate holder 4 heated by the heater 41 to a temperature from about 600.degree. to about 650.degree. C. Then, the valve a is closed. Subsequently, a carrier gas, i.e. , hydrogen (H.sub.2) is supplied from the gas source 21d1 into the bubbler 21a1 storing liquid pentaethoxytantalum (Ta(OC.sub.2 H.sub.5).sub.5) for bubbling pentaethoxytantalum, and the generated pentaethoxytantalum gas is supplied into the process chamber 1. In this operation, the bubbler 21a1 is heated to a predetermined temperature by the temperature controller 21g1, and, if necessary, the heater 21h is turned on for maintaining the intended gaseous state. The different gas supply unit 22 supplies an oxygen (O.sub.2) gas. The bubbling may be performed, for example, with an inert gas such as a helium (He) gas or an argon (Ar) gas or a hydrogen gas, and a hydrogen gas may be supplied via another passage from the different gas supply unit 22.
The gas thus introduced is decomposed at the vicinity of the heated substrate S10, so that an intended film is deposited on the surface of the substrate S10. If the film material stored in the bubbler is gaseous at room temperature, the material may be cooled to an appropriate temperature by the temperature controller 21g1.
In addition to the ditantalum pentoxide film, the apparatus described above can also form various kinds of ferroelectric films. For example, it can form a lead monoxide (PbO) film from tetraethyllead (Pb(C.sub.2 H.sub.5).sub.4) (or lead dipivalylmethanate (Pb(DPM).sub.2) and oxygen (O.sub.2) gases, a titanium dioxide (TiO.sub.2) film from titanium tetrachloride (TiCl.sub.4) (or pentaethoxytitanium (Ti(OC.sub.2 H.sub.5).sub.5) or tetraisoproxytitanium (Ti(O-i-C.sub.3 H.sub.7).sub.4)) and oxygen (O.sub.2) gases, a zirconium oxide (ZrO.sub.2) film from tetra-tert-butoxyzirconium (Zr(O-t-C.sub.4 H.sub.9).sub.4) and oxygen (O.sub.2) gases, a barium oxide (BaO) film from diethoxybarium (Ba(OC.sub.2 H.sub.5).sub.2) and oxygen (O.sub.2) gases, a strontium oxide (SrO) film from diethoxy strontium (Sr(OC.sub.2 H.sub.5).sub.2) and oxygen (O.sub.2) gases, and a lanthanum oxide (La.sub.2 O.sub.3) film from lanthanum dipivalylmethanate (La(DPM).sub.2) and oxygen (O.sub.2) gases. Among the aforementioned film materials, tetraethyllead, titanium tetrachloride, pentaethoxytitanium and tetraisoproxytitanium are liquid at room temperature, and thus are supplied into the process chamber 1 by bubbling them. Lanthanum dipivalylmethanate, diethoxybarium, diethoxy strontium and lanthanum dipivalylmethanate are solid at room temperature, so that they are solved, for example, in alcohol such as ethanol for bubbling them. Tetra-tert-butoxyzirconium is gaseous at room temperature, so that it may be cooled to an appropriate temperature, if necessary or desirable.
If a composite oxide film, such as a strontium titanate (SrTiO.sub.3) film, barium metatitanate (BaTiO.sub.3) film or zirconium oxide titanium oxide lead (Pb(Zr,Ti).sub.x O.sub.2) film is to be formed, two or more bubblers are used to bubble several kinds of film material liquids containing film forming elements for supplying them to the process chamber 1.
However, the film deposition by the plasma-CVD and thermal-CVD described above presents the following problems.
First, the problem caused by the plasma-CVD will be described below.
According to the plasma-CVD method and apparatus, powder particles are generated due to gaseous phase reaction in the plasma, and they form dust which adheres to or are mixed into the film formed on the surface of the substrate, resulting in deterioration of the film quality.
For example, if an amorphous hydrogenated silicon (will be also referred to as "a-Si:H") film is to be formed from the material gas of monosilane (SiH.sub.4), plasma is formed from the gas for film deposition, and, at the same time, high order silane is generated due to the reaction in the gaseous phase and is polymerized to generate the dust.
In order to prevent the dust from adhering to and mixing into the film, the plasma-CVD apparatus has generally been devised to suppress generation of the particles in various manners, and more specifically, devices are applied to a system for transferring the substrate to the process chamber, arrangement of the substrate in the process chamber, materials and others of respective members and film deposition conditions (such as a magnitude of the applied power for plasma deposition, a gas pressure during deposition and a deposition temperature). Also, cleaning is generally effected on the interior of the process chamber, the electrodes and the substrate transferring system during intervals between operations of the plasma-CVD apparatus.
However, even if conditions are determined to suppress the particle generation, the particles inevitably adhere to the substrate during film deposition. For example, when the parallel plated plasma-CVD apparatus is used to form an amorphous hydrogenated silicon (a-Si:H) film on the substrate from the material gas of monosilane (SiH.sub.4), the particles inevitably adheres to the substrate even if optimum conditions are set to suppress the particle generation.
Meanwhile, as the applied power for plasma formation is increased for increasing a deposition rate, the amount of generated particles increases. Therefore, the applied power can be increased only to a limited value in view of suppression of the particle generation, so that the deposition rate cannot be increased sufficiently.
In order to suppress the particle generation, the following manner has also been proposed, for example, in Japanese Laid-Open Patent publication Nos. 5-51753 (1993) and 5-156451 (1993). For generating the plasma from the material gas, a first pulse modulation at a modulation frequency not higher than 1 kHz (e.g., in a range from 400 Hz to 1 kHz) is effected on an rf-power of a predetermined frequency, and further, a second modulation at a cycle period shorter than that in the first pulse modulation is effected in a superimposed manner on the above first modulated power. Further, a third pulse modulation at a cycle period shorter than that in the second pulse modulation is effected in a superimposed manner on it. By applying the rf-power thus produced, film deposition can be carried out without suppressing generation of radicals which contribute to the film deposition, while suppressing the particle generation. This plasma-CVD utilizes the facts that the radicals contributing to the film deposition have a relatively long life and the radicals causing dust particles have a relatively short life, and can suppress the particle generation and improve the deposition rate to some extent. However, the suppression of the particles and the improvement of the deposition rate can be achieved only to a limited extent and cannot be achieved sufficiently.
Also in the above case, the magnitude of the applied power is limited to some extent so as to suppress the particle generation in view of the fact that the increased power increases the numbers of generated particles. Therefore, the deposition rate is not sufficiently high.
Particles are generated not only by the plasma-CVD for forming the amorphous silicon film and silicon nitride film but also by the plasma-CVD for forming another kind of film such as a carbon film.
The carbon film has such characteristics that its hardness increases in accordance with increase of the substrate processing temperature for film deposition. Accordingly, when coating with hard carbon films is effected, for example, on cutting tools or machine parts in order to improve their surface hardness, the substrate processing temperature is set to 500.degree. C. or more. However, an ECR plasma-CVD or a heat filament CVD is generally employed instead of the parallel plated plasma-CVD apparatus for setting the substrate processing temperature to a high value as described above. According to the ECR plasma-CVD, a substrate can be heated up to about 800.degree. C. by positioning it at an ECR resonance point. Owing to the deposition process under such a high temperature condition, a DLC film of good quality can be easily formed as compared with the film deposition with the parallel plated plasma-CVD apparatus, and the ECR plasma-CVD can also produce a diamond film. According to the heat filament CVD, the substrate can be heated up to about 900.degree.-1100.degree. C. by radiant heat. Owing to such a high-temperature deposition, a DLC film and a diamond film having good quality can be produced easily. Deposition under the high-temperature condition by the ECR plasma-CVD and heat filament CVD can suppress the particle generation as compared with the deposition at the relatively low temperature by the parallel plated plasma-CVD apparatus.
For deposition of the carbon film, therefore, it is preferable to employ the ECR plasma-CVD or heat filament CVD in many cases if the substrate has a heat resistance. However, if the substrate is made of a material such as synthetic resin not having a sufficient heat resistance, the deposition must be performed at a relatively low temperature by the parallel plated plasma-CVD apparatus. In the latter case, the particle generation cannot be suppressed sufficiently, and further, the deposition rate can be increased only to a limited value because the particle generation is promoted as the applied power is increased for increasing the deposition rate.
If the plasma-CVD apparatus, for example, shown in FIG. 17 or FIG. 18, uses a material gas containing chlorine (Cl), and more specifically, if the apparatus forms an amorphous silicon film, silicon nitride film or the like from relatively safe silicon tetrachloride (SiCl.sub.4), or forms a titanium nitride film from titanium tetrachloride (TiCl.sub.4), a problem of the particle generation arises, and the chlorine is liable to remain in the deposited film. In order to avoid this, the substrate must be maintained at a high temperature of about 750.degree. C. or more during deposition, in which case the quality, e.g., of the amorphous silicon film deteriorates due to the high temperature. This problem is caused not only in the case of use of chlorine compound but also in the case that the film deposition gas contains halogen compound due to the fact that the substrate must be maintained at a high temperature for avoiding remaining of halogen in the film.
Further, if the substrate is cleaned by exposing it to plasma which is formed from a pretreatment gas, as is done by the plasma-CVD apparatus shown in FIG. 18, such a problem arises that the particles are generated during film deposition after the cleaning, and further the cleaning itself causes such a problem that the process of cleaning the substrate by forming the plasma from the pretreatment gas cannot be performed efficiently. Additionally, since it is difficult to clean uniformly the substrate, the film deposited on the cleaned substrate cannot have a sufficiently uniform thickness.
Problems relating to a ferroelectric film by the thermal-CVD will be described below.
When forming the film by the thermal-CVD apparatus shown in FIG. 19, a supplying ratio of the film material gases supplied to the process chamber is not equal to a composition ratio of the deposited ferroelectric film, so that the composition ratio and hence quality of the deposited film cannot be controlled easily.
If the substrate is maintained at a high temperature of about 650.degree. C. or more, which is preferable for improving the film quality, atoms such as lead (Pb) atoms having a high vapor pressure are liable to escape into the atmosphere. Therefore, if organic compound containing such an element is used as the film material, the required amount of the material and hence the film formation cost increase, and further it is difficult to control uniformity of the film thickness.
Further, the deposition rate is low, and, for example, the zirconium oxide titanium oxide lead (Pb(Zr,Ti).sub.x O.sub.2) described above cannot be deposited at a rate exceeding about 60 .ANG./min.
In order to prevent the above problem relating to deposition of the ferroelectric film, a plasma-CVD apparatus, for example, shown in FIG. 20 may be employed, which was developed by the inventors during development of the invention.
This apparatus differs from the thermal-CVD apparatus shown in FIG. 19 in that a ground electrode 7 also serving as a substrate holder is provided instead of the substrate holder 4, and an rf-electrode 5 is opposed to the electrode 7 in the process chamber 1. The electrode 7, which serves as a power application electrode, applies an rf-power to a film material gas introduced between the electrodes 5 and 7 for forming the plasma, and is connected to an rf-power source 52 via a matching box 51. The electrode 7 is provided with a high-temperature plate heater 71 for heating the substrate S10 to a deposition temperature.
In the operation of forming, for example, a ditantalum pentoxide film by the aforementioned plasma-CVD apparatus shown in FIG. 20, the substrate S10 transferred into the process chamber 1 is mounted on the electrode 7, and then, predetermined amounts of pentaethoxytantalum gas and oxygen gas are introduced into the process chamber 1 from the gas supply unit 2 similarly to the case of forming the ditantalum pentoxide film by the apparatus shown in FIG. 19. Also, the rf-power source 52 applies the rf-power to the rf-electrode 5. Thereby, the plasma is formed from the introduced gases, and the ditantalum pentoxide film is deposited on the surface of substrate S10 in the plasma.
Other structure and operation are the same as those of the apparatus shown in FIG. 19. The same portions and parts as those in the apparatus shown in FIG. 19 bear the same reference numbers.
Even in the plasma-CVD apparatus described above, however, particles generated by gaseous phase reaction in the plasma adhere onto the film deposited on the substrate and/or are mixed into the film, resulting in deterioration of the film quality. Accordingly, it is preferable or necessary to restrict the applied power for suppressing the particle generation in view of the fact that increase of the applied power promotes the particle generation. However, this reduces the deposition rate.
Further, defects occur at the vicinity of the boundary between the substrate and the film, due to plasma damage, so that the dielectric constant of the film decreases to some extent.